Problems associated with the forgery or counterfeiting of various types of documents are long standing and well known. For example, forgery of transportation tickets, negotiable instruments, currency or other documents of value is a continuing and ongoing problem to issuers of such documents.
The widespread use of plastic credit or debit cards has created, yet, another set of authentication and verification problems. It is very common for such cards to include pre-recorded magnetic stripes which include transaction related information. This information can include account numbers, credit limits and/or personal identification codes.
However, such cards have been especially susceptible to forgery in view of the fact that the magnetic encoding is almost always based on one or more publicly known standards. One such standard, ANSI 4.16-1983 is utilized in connection with many pre-recorded magnetic stripes associated with such cards.
Multi-use transportation documents present yet another type of authentication problem. Such documents are magnetically alterable at the time of use to decrease the remaining value of the card. However, if an original, unused document can be both physically and magnetically duplicated to create a useable counterfeit document, the issuing agency can loose substantial proceeds.
Various systems are known which can be utilized to create and authenticate verifiable documents or credit cards. Some of the known systems are magnetically based. Other are optically based.
One known type of system is disclosed in U.S. Pat. No. 4,837,426 to Pease et al. entitled "Object Verification Apparatus And Method" which is assigned to the Assignee of the present invention. The disclosure and figures of the Pease et al. patent are hereby incorporated herein by reference.
In the system of the Pease et al. patent, a randomly varying magnetic character is measured and used to create a verification key which can be carried on the document. The verification key of the Pease et al. system is a result of processing sensed values of the random magnetic characteristic and creating a single key for the entire document.
A different magnetically based security system is disclosed in U.S. Pat. No. 4,806,740 to Gold et al. entitled "Magnetic Characteristic Identification System". As in the case of the Pease et al. system, the system of the Gold et al. patent creates a verification key for the document which can be carried thereon.
Optically based security systems are disclosed in U.S. Pat. No. 4,423,415 to Goldman entitled "Noncounterfeitable Document System". In one embodiment disclosed in the Goldman system, the translucency of a region of a document is utilized as the measured randomly varying characteristic. Alternately, the Goldman patent also discloses the use of reflectivity for the same purpose. Whether translucency or reflectance are utilized, the system of the Goldman patent also creates a single verification key for a given document.
While known systems appear to be effective with respect to verification of certain types of objects, in each instance, the verification key created for an object is the result of processing measured characteristic values over a region of the object. From these measured and processed characteristic values, a verification key is generated for the entire region and hence the object.
There are times where it would be desirable to be able to verify the authenticity of only a portion of the object. The known systems, need to have the entire region of the random characteristic available. As a result, the known systems are unable to determine if a portion of a document is in fact authentic.
Hence, there continues to be a need for authentication/verification systems of more general applicability then has previously been known. Preferably, such systems would be usable to properly authenticate a portion of an object. In addition, preferably such systems would be readily usable with magnetically based randomly varying characteristics as well as optically based characteristics.